CELSIUS AND FAHRENHEIT SCALE DIGITAL THERMOMETER USING IC P89V51RD2
TABLE OF CONTENT
Fahrenheit scale digital thermometer is a temperature indicator which displays temperature in Fahrenheit scale. It consists of two sections. One is that which senses the temperature. This is a temperature sensor LM 35. The other section converts the temperature value into a suitable number in Celsius scale which is done by the ADC0804. The temperature sensed in Celsius scale is converted into the Fahrenheit scale temperature just by using the Celsius to Fahrenheit conversion formulae. This project also uses 8051 microcontroller (AT89C51). Keywords— Celsius, Fahrenheit, ADC
A digital thermometer can be easily made by interfacing a temperature sensor to the microcontroller AT89C51. The temperature sensor used in the project is LM35. The LM 35 IC generates a 10mV variation to its output voltage for every degree Celsius change in temperature. The Output of the temperature sensor is analog in nature so we need an analog to digital convertor for converting the analog input to its equivalent binary output. The ADC 0804 is the analog to digital convertor IC used in the project. 0804 is a single channel convertor which converts the analog input up to a range of 5V to an equivalent 8-bit binary output.
Fig 2.1-Block Diagram
The block diagram of the thermometer consists of a temperature sensor, adc and a microcontroller. The LM35 IC senses the temperature. The adc converts this analog input voltage from the sensor to required digital form which is then given to the microcontroller which in turn is programmed in a manner to drive the lcd to display the temperature in Celsius and Fahrenheit form. The code for the respective program was written.LM35 gives ouput voltage corresponding to Celsius temperature.So a provision was made in the program itself to convert Celsius temperatures to farhenit temperatures and display both on the lcd.
Pin Diagram of LM35
LM35: LM35 is a precision IC temperature sensor with its output proportional to the temperature (in oC). The sensor circuitry is sealed and therefore it is not subjected to oxidation and other processes. With LM35, temperature can be measured more accurately than with a thermistor. It also possess low self heating and does not cause more than 0.1 oC temperature rise in still air. The operating temperature range is from -55°C to 150°C. The output voltage varies by 10mV in response to every oC rise/fall in ambient temperature, i.e., its scale factor is 0.01V/ oC.
ADC 0804: ADC0804 is a very commonly used 8-bit analog to digital convertor. It is a single channel IC, i.e., it can take only one analog signal as input. The digital outputs vary from 0 to a maximum of 255. The step size can be adjusted by setting the reference voltage at pin9. When this pin is not connected, the default reference voltage is the operating voltage, i.e., Vcc. The step size at 5V is 19.53mV (5V/255), i.e., for every 19.53mV rise in the analog input, the output varies by 1 unit. To set a particular voltage level as the reference value, this pin is connected to half the voltage. For example, to set a reference of 4V (Vref), pin9 is connected to 2V (Vref/2), thereby reducing the step size to 15.62mV (4V/255). ADC0804 needs a clock to operate. The time taken to convert the analog value to digital...
Bibliography: a) IEEE MAGAZINE
b) ELECTRONICS FOR U
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